Environmental concerns during the past decade and more have caused many governing bodies to issue regulations limiting the VOC of coating compositions. In response to these regulations, the coating industry has turned to powder coating formulations which contain essentially no volatile organic compounds and to water-based coating compositions. Because of the corrosive nature of water-based compositions, they must be shipped in plastic containers or in specially coated steel containers. Special equipment such as stainless steel tanks, lines, and spraying apparatus must also be used. The typical commercially available solvent-borne coating compositions have a VOC of about 5.0 pounds or more per gallon. While it would be desirable to lower the VOC of such compositions for environmental reasons, the practical difficulty is that the viscosity would be generally too high for easy applicability to a chosen substrate.
Modern automobiles use significant and increasing amounts of plastic and elastomeric components and thus the demand for coatings having a high degree of elasticity, toughness, and weatherability has been increasing steadily. Poly (ester-urethane) polyol resins when cured with an aminoplast provide suitable elastomeric coatings but these are expensive. Polyester resin compositions may also be cured with an aminoplast to yield coatings but their elasticity and weatherability generally have not been satisfactory. The formulation of polyester resin coating compositions having the demanded properties is made significantly more difficult when the polyester must also have properties which allow it to be shipped and pumped in a water-free state but readily reducible with water to a sprayable viscosity at the point of use.